diff --git a/src/Tiny_httpd.ml b/src/Tiny_httpd.ml
index f20d91ee..3ff6347a 100644
--- a/src/Tiny_httpd.ml
+++ b/src/Tiny_httpd.ml
@@ -1,9 +1,14 @@
+type input_stream = (bytes -> int -> int -> int) * (unit -> unit)
+(** An input stream is a function to read bytes into a buffer,
+    and a function to close *)
 
-(** An input stream. *)
-type input_stream = {
-  ic: in_channel;
-  mutable buf: bytes;
-}
+type output_stream = (bytes -> int -> int -> unit) * (unit -> unit) * (unit -> unit)
+(** An output stream is a function to output bytes, a function to [flush],
+    and a function to close. *)
+
+module Input_stream = struct
+
+end
 
 exception Bad_req of int * string
 let bad_reqf c fmt = Printf.ksprintf (fun s ->raise (Bad_req (c,s))) fmt
diff --git a/src/Tiny_httpd.mli b/src/Tiny_httpd.mli
index 1a00f5b0..ab94e536 100644
--- a/src/Tiny_httpd.mli
+++ b/src/Tiny_httpd.mli
@@ -1,3 +1,24 @@
+type input_stream = (bytes -> int -> int -> int) * (unit -> unit)
+(** An input stream is a function to read bytes into a buffer,
+    and a function to close *)
+
+type output_stream = (bytes -> int -> int -> unit) * (unit -> unit) * (unit -> unit)
+(** An output stream is a function to output bytes, a function to [flush],
+    and a function to close. *)
+
+module Input_stream : sig
+  type t = input_stream
+
+  val of_chan : in_channel -> t
+  val of_string : string -> t
+  val of_bytes : bytes -> t
+end
+
+module Output_stream : sig
+  type t = output_stream
+
+  val of_chan : out_channel -> t
+end
 
 module Meth : sig
   type t = [